The remote host is missing an update to horde3 announced via advisory DSA 1098-1. Michael Marek discovered that the Horde web application framework performs insufficient input sanitising, which might lead to the injection of web script code through cross-site scripting. The old stable distribution (woody) does not contain horde3 packages.
For the stable distribution (sarge) this problem has been fixed in version 3.0.4-4sarge4. For the unstable distribution (sid) this problem has been fixed in version 3.1.1-3. We recommend that you upgrade your horde3 package. https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201098-1